With their decreased availability and adverse impact to the environment, fossil fuels and other conventional energy sources are continually declining in popularity while clean, renewable energy source have seen rapid growth. In the coming years, as these fossil fuels continue to become scarce and as knowledge regarding the environmental impact of such energy sources becomes available, the demand for clean, renewable energy will continue to increase. One such source of clean, renewable energy is wind power. For example, kinetic energy from wind may be transmitted into electricity using, e.g., a wind turbine. Accordingly, electricity may be produced without burning any of these costly, environmentally hazardous fossil fuels.
Wind turbines create power proportional to the swept area of their blades. Thus, by increasing the length (e.g., span) of wind turbine blades, more energy may be produced. However, the choice of rotor attributes for a wind turbine, such as its diameter, is a design trade-off between longer blades for more energy production in low winds and shorter blades for load limitation in high winds. A wind turbine having longer blades will increase the swept area, which in turn produces more power. But at high wind speeds, a wind turbine having longer blades places greater demands on the components and creates more situations where the turbine must be shut down to avoid damaging components. Even in situations where the average wind speed is not high enough to cause damage, periodic wind gusts may change both the speed and direction of the wind and apply forces that may be strong enough to damage equipment.
Approaches with varying levels of success have been attempted in achieving higher power, fewer shut downs, and less instances of damage to components. For example, pitch control has been used to vary the pitch of the blade (i.e., the angle of the blade). On a pitch controlled wind turbine, an electronic controller on the turbine checks the power output of the turbine. When the power output exceeds a certain threshold, the blade pitch mechanism turns the rotor blades to reduce the loads on the rotor blades. The blades are later turned back when the wind drops again. However, pitch control can be fairly slow to respond to changes in the wind and is relatively ineffective to loads imparted by sudden wind gusts.
Stall control is another approach that has been used in an attempt to achieve higher power, and to reduce shut downs and damage to components. In passive-type stall controlled wind turbines, the rotor blades are mounted to the hub at a fixed angular orientation. The stall control is achieved passively by the shape of the blade being such that the blade goes into aerodynamic stall (destroying lift) when the wind speed exceeds a certain threshold. Active-type stall controlled wind turbines exist. In such systems, the rotor blades are adjusted in order to create stall along the blade. However, both types of stall control systems can be difficult to optimize and slow to respond, and may suffer from lower predictability of results than desired. These drawbacks are magnified in conditions with erratic winds and wind gusts.
Variable length rotor blade systems have also been used as an attempt to achieve higher power, and experience fewer shut downs and less damage to components. In such systems, the wind turbine rotor blades are telescopic so that their length can be adjusted based on the wind speed. Such provides advantages in that the rotor blades can be extended to provide higher output in low wind conditions and retracted to lower loads in high wind conditions. U.S. Pat. No. 6,902,370, titled “Telescoping Wind Turbine Blade” and which is hereby incorporated by reference in its entirety, discloses a wind turbine system having telescoping wind turbine rotor blades. While variable length rotor blade systems have certain advantages, they may suffer drawbacks in erratic wind conditions or may be too slow to respond when experiencing a wind gust.
More recently, deflectors have been used to control loads on a wind turbine's components. For example, deflectors have been used to disrupt the airflow on a wind turbine blade thus reducing lift and the corresponding load placed on the wind turbine components. For example, U.S. Pat. No. 8,267,654, titled “Wind Turbine with Deployable Air Deflectors” and which is hereby incorporated by reference in its entirety, describes the use of deflectors on a wind turbine blade to control loads. These deflectors are deployed when a sensor or other component senses power production, speed, acceleration, loads, or the like has exceeded a threshold value, and the deflectors are thus deployed to bring the sensed power production, speed, acceleration, loads, etc. back within the threshold.
In some instances, multiple deflectors are used on a wind turbine and/or a wind turbine blade to control loads. For example, in some embodiments, multiple deflectors are arranged along the length of a wind turbine blade. Accordingly, one or more of the multiple deflectors may be deployed to control load as discussed above. However, in such embodiments, some deflectors may be deployed more than others, leading to hyperactivity of some (and thus early failure) and under usage of others. Further, depending on a spanwise location of each deployed air deflector, for certain conditions some deflectors may be less effective than others, leading to more than necessary deflectors being deployed (and thus ultimately increasing the duty cycle total for the system as a whole).
As electricity continues to become a more valuable commodity, and as wind turbines present an environmentally-friendly solution to solve electricity shortage problems, a wind turbine design that overcomes the aforementioned drawbacks and provide increased power and decreased turbine shut downs and damage to components is thus desirable.